Embodiments of the present invention relate to a linearity power amplification device and, more specifically, to a linearity power amplification device using a feedforward-predistortion system to eliminate error signals.
High Linearity power amplifiers are very important in MR systems. Its power is generally more than 16 KW. High power amplifiers work near the saturation region having non-linearity characteristics to produce the maximum output. However, in the case of the high power amplifier with multi-carrier inputs, generally distortions would be caused. Therefore, the amplifier's quality is deteriorated.
U.S. Pat. No. 6,104,241 discloses a linearity power amplifier arrangement. The linearity power amplifier arrangement comprises: an RF input port to which an RF input signal is applied, an RF output port from which an RF output signal is derived, first and second RF signal processing paths coupled between the input and output ports and containing first and second RF power amplifiers, and an output signal combiner.
The first RF signal processing path includes a first RF signal vector modulator, that is controllably operative to adjust one or more parameters of a first RF input signal component applied to the first RF power amplifier.
The second RF signal processing path includes a predistortion unit and an intermodulation distortion (IMD) extraction circuit. The predistortion unit contains a second RF signal vector modulator and a predistorter, that is controllably operative to predistort a second RF input signal component applied to the second RF power amplifier in a manner that compensates for the presence of distortion energy applied to the second RF power amplifier that is not applied to the first RF power amplifier. The IMD extraction circuit is coupled to the RF input port and to an output of the first RF power amplifier and is operative to generate the second RF input signal component as a combination of the RF input signal and an IMD component.
The output signal combiner is coupled to outputs of the first and second RF power amplifiers and the output port, and is operative to produce the RF output signal as a composite RF output signal.
However, for the linearity power amplifier arrangement in the U.S. Pat. No. 6,104,241, its cost is very high and it is difficult to be applied to a real circuit. Moreover, it only can support 2-way amplifiers.
Furthermore, if the gain of auxiliary amplifier is the same as that of the main amplifier, the matching circuit is complicated and difficult to be implemented. If the gains of both amplifiers are different, the adjacent channel power ratio (ACPR) would be degraded.